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This Used To Be a Death Sentence, but No More — So Long as It's Caught Early

feline leukemia virus

Story at-a-glance -

  • Thankfully, a diagnosis of feline leukemia virus (FeLV) is no longer a death sentence for cats
  • Cats exposed to FeLV will respond in one of three ways: some will avoid infection, some will develop a latent infection and some will become permanently infected
  • There are several symptoms as the disease progresses, including loss of appetite, weight loss and secondary infections
  • There is no cure for FeLV, but there are many things you and your veterinarian can do to help your cat have an excellent quality of life
  • The goal is to identify FeLV before a cat becomes symptomatic and then offer lifetime immune system support

By Dr. Karen Shaw Becker

Not long ago, a diagnosis of feline leukemia virus (FeLV) in a cat was a death sentence. Thankfully, these days most cats diagnosed with FeLV can live long, healthy lives with proper care. And there are lots of kitties living with the virus. A recent study of 62,301 cats from 1,396 veterinary clinics and 127 shelters determined a FeLV prevalence rate in North America of 3.1 percent, or about 3 million cats.1

There are actually three types of feline leukemia virus: FeLV-A, FeLV-B and FeLV-C. Cats can be infected with one, two or all three types.

  • FeLV-A occurs in every cat infected with feline leukemia, and it severely compromises the immune system
  • FeLV-B occurs in about half of infected cats, and causes tumors and other abnormal tissue growths
  • FeLV-C occurs in only about 1 percent of FeLV-infected cats and causes severe anemia

How the Virus Spreads and Cats at Highest Risk for Infection

The FeLV virus is shed in bodily fluids including saliva, nasal secretions, urine, feces and blood. It is transmitted through direct contact, primarily mutual grooming, and use of shared litterboxes, food and water bowls.

FeLV can also be passed from a mother cat to her kittens either in utero, or while nursing. In addition, it can be transmitted through the bites and scratches of an infected cat. It takes large amounts of virus to infect an adult cat, so prolonged contact or a bite is necessary for transmission.

It’s estimated that about 2 to 3 percent of otherwise healthy cats are infected with feline leukemia. The rate jumps to 13 percent or more in kitties who are sick, very young or otherwise vulnerable to infection. At highest risk for infection are:

  • Kittens born to infected mothers
  • Cats living with infected cats or cats of unknown infection status
  • Cats allowed outdoors where they can be bitten by an infected cat

Stages of Infection

There are two stages of a FeLV infection. The early stage is called primary viremia. During this stage, some kitties are able to fight off the virus, stopping it from progressing to the second stage, called secondary viremia. This stage features persistent infection of bone marrow and other tissue, and is considered irreversible. Two to four weeks after exposure to the feline leukemia virus, cats typically respond in one of a few ways:

  • Some kitties will not become infected due to inadequate exposure and/or a good immune system response.
  • Some will develop a latent or regressive infection, meaning they didn’t completely clear the virus, but their immune system can hold it in check. These cats typically show no signs of infection and do not shed the virus in their saliva or other bodily fluids.
  • Kitties that do not launch an adequate immune response will become permanently infected with FeLV. These cats will shed large amounts of the virus and begin to develop FeLV-associated conditions within a few years. This happens most often when exposure occurs before a kitten is 8 weeks old.

Symptoms of FeLV

FeLV has a number of negative effects on a cat’s body. It is the most common cause of feline cancer, it can cause various blood disorders and it can so decimate the immune system that it can’t defend the body against other infections. Common pathogens found in the environment that cause no harm to healthy animals can cause severe illness in a FeLV-positive kitty. Secondary infections are the cause of many of the diseases associated with FeLV.

Early in the infection, many cats show no signs of illness. As the disease progresses, however, a kitty’s health may gradually deteriorate or she may have recurring illnesses followed by periods of relatively good health. There is a long list of symptoms associated with this viral infection, including:

Loss of appetite

Inflammation of the gums (gingivitis) and mouth (stomatitis)

Slow, progressive weight loss followed by severe wasting late in the disease process

Infections of the skin, urinary bladder and upper respiratory tract

Poor coat condition

Persistent diarrhea

Enlarged lymph nodes

Seizures, behavior changes and other neurological disorders

Persistent fever

A variety of eye conditions

Pale gums and other mucus membranes

Spontaneous abortions in pregnant females, and other reproductive problems

There are two types of blood tests for feline leukemia that look for a specific protein component of the virus. The ELISA (enzyme-linked immunosorbent assay) test detects FeLV in both the primary and secondary stages, and can be performed at the veterinary clinic. The IFA (indirect immunofluorescent antibody assay) test picks up secondary viremia only, so the majority of kitties who test positive will be infected for life. This test must be sent out to a diagnostic laboratory and is often used to confirm a positive ELISA test for FeLV.

Treatment and Management of FeLV-Positive Cats

There is no specific treatment for kitties with FeLV, however, any existing secondary infections will need to be treated. I recommend lymphocyte T-cell immunomodulator injections (T-cyte), which isn’t a cure, but can help maintain quality of life for FeLV kitties.

FeLV-positive cats should be kept indoors, which will prevent the spread of the virus to other cats, while also reducing the risk that your kitty will be exposed to pathogens her immune system may not be able to fight off. FeLV-positive cats should not reproduce and should never be vaccinated for anything, ever.

Infected kitties are best nourished with a nutritionally balanced, species-appropriate, fresh food diet. Unless your kitty has a low white blood cell count — in which case I recommend cooked fresh food — a raw diet is fine, and can do wonders to cellularly nourish your cat.

You can also select a commercially available raw food diet that has been high-pressure pasteurized; this is a great choice for kitties in all stages of the virus, and removes the fear of feeding raw food for veterinarians who aren’t fresh-food friendly. Cats with FeLV should see the veterinarian at least twice yearly to review the health of their eyes, gums, skin and lymph nodes, and to check their weight. At one of the two yearly visits, bloodwork and urinalysis should be performed.

Careful, consistent monitoring of your FeLV-positive kitty’s health and behavior is extremely important so that you can notify your vet right away of any changes. I’ve had good success keeping my FeLV-positive patients very healthy using a variety of natural supplements to support the immune system, including:

Standard Process Feline Immune System Support and Feline Whole Body Support

Medicinal mushrooms


IV vitamin C therapy

Ozone therapy

Kyosenex thymus extract

Chinese herbs

FeLV homeopathic nosodes

I’ve also had good success keeping FeLV-infected cats who have not yet developed symptoms of the disease, asymptomatic.

Preventing FeLV and the Outlook for Infected Cats

Sadly, FeLV-positive kitties whose immune systems aren’t supported can succumb to a secondary disease within two or three years of becoming infected. Cats that acquire one or more serious FeLV-related illnesses, kitties with persistent fevers and weight loss, and those with cancer, can be expected to have a much shorter survival time as well.

The goal should always be to identify feline leukemia before a kitty becomes symptomatic and then offer lifetime immune system support. In these cases, many FeLV-positive cats can live a completely normal life. The only foolproof way to keep your cat safe from FeLV is to prevent exposure to the virus. This obviously means keeping her away from potentially infected cats.

If your cat goes outdoors, it should be under your close and constant supervision, or in a safe, secure outdoor enclosure — one that prevents other cats not only from getting in, but from being able to bite or scratch your kitty through the sides or top of the enclosure. If you have an uninfected cat, never allow untested or at-risk kitties to mingle with yours. Keep FeLV-positive cats separate from viral-free cats.

I don’t recommend the FeLV vaccine, as it’s often ineffective and has been linked to the development of vaccine-associated sarcomas in cats. I also don’t recommend viral positive cats receive any other vaccines, which stress the immune system.